MRI protocol development at clinical field strengths

In the last three decades MRI has revolutionized our understanding of the human
body and how disease can affect it. Especially, for studies of the brain,
joints, spinal cord, and the heart, MRI has opened new avenues for diagnosis of
disease and has increased our basic understanding of anatomy, pathology,
physiology and metabolism in humans. It has become one of the central
modalities in every radiological clinic. MRI is a continuously developing
modality, requiring continuous optimization and implementation of newly
emerging techniques.
The rapid expansion of MRI applications over the last 30 years can be
attributed mostly to improved hardware and acquisition techniques.
Interestingly, this has increased the number of different contrasts that can be
achieved with MRI. First, anatomical imaging was developed, followed by
angiographic techniques and spectroscopic techniques that enable the
measurement of concentration of metabolites. Around 1990, it was discovered
that MRI could enable the identification of the location of brain activation,
which revolutionized cognitive research. Later, physiological techniques were
proposed to measure tissue perfusion, blood volume, and oxygenation. In recent
years, new techniques have been proposed, like pH measurement, myelin imaging,
iron quantification, that are not yet accepted by the radiologically clinic,
but are already employed in clinical research. To further optimize existing
techniques, to bring recently proposed techniques towards clinical research and
diagnostics, and to propose even newer ones, MR physics research will remain
necessary. This will also further enhance the clinical research within the LUMC.
The MR physics research in the LUMC has increased considerably with the
installation of the 7 Tesla MRI scanner in 2006. The investigational nature of
this scanner made it mandatory to not only invest in new hardware, but also in
MR physics researchers to further develop ultra-high field MRI. These
researchers want to extend their activities also to lower, clinically used
field strengths for three reasons:
1. Many clinical studies are running on these lower field strengths, because of
their robustness, easier patient handling, less contra-indications,
availability of scan time, and their national availability (i.e. multi-center
studies). Therefore, it is essential that new or improved techniques do not
only run on the 7Tesla scanner, but also on lower field strengths to enable
their application in clinical studies
2. Worldwide 99% of the MR research is still performed on these lower field
strengths. For the impact of the developed techniques it is therefore necessary
to prove their performance on these field strengths
3. Whereas for some techniques 7Tesla is clearly showing huge improvements, for
other applications it will require much more hardware and software developments
before successful application will be feasible. For some of these techniques it
is better to first optimize and develop methods at lower field strengths and
only after this additional experiences (maybe) move to 7Tesla.

To further optimize MRI techniques and to develop new MRI techniques that will
enable state-of-the-art clinical and cognitive research and will lead to
improved patient care on MR scanners of clinical field strengths (<4 Tesla).
Typical applications that will be studied are anatomical imaging of the vessel
wall, hemodynamic imaging, susceptibility weighted imaging, quantitative MRI
techniques, MR spectroscopy, fMRI and DTI techniques.

Studies will be performed by qualified personnel (i.e. having a *scan brevet*
as provided by the MR safety committee of the department of Radiology) and
according to the standards of the Radiology department (participants will
therefore in principle receive double ear protection (ear plugs and head
phone), will be allowed to listen to music when possible, etc).
An MR session for this study will be approximately 1 hour. The volunteer will
be informed prior to the MRI examination of the anticipated duration and can of
course always stop the study without any explanation. For some studies it will
be necessary to record respiratory and/or cardiac signals to minimize artifacts
in the MRI images arising from the moving heart and lungs. These physiological
signs are recorded with equipment provided by the scanner manufacturer (Philips
Healthcare) and are an integral part of the MRI scanner. Furthermore, it might
be necessary for the volunteer to perform a small task (looking at a flickering
checkerboard, fingertapping, etc) to evoke neuronal activation. During the
session, the volunteer will always be in direct contact with the MRI operator
by means of an alarm bell (the volunteer will be in full control) and an
intercom system. The operator will inform the subject about the progress of the
session and will check on the volunteer*s well-being. Whenever the subject
feels uncomfortable, the session will be ended immediately. At the end of the
session a verbal post-imaging interview will be held to identify discomfort of
the study. If the subject indicates significant discomfort, the radiologist on
duty is informed and a side-effects form is completed. This form is sent to the
MR safety committee of the Department of Radiology and if the discomfort is
considered to be serious they forward the form to the CME.
It should be noted that MRI at clinical field strengths is considered to be
absolutely safe when operated correctly and that it is already employed in the
LUMC for more than 25 years without any serious damage to patients, workers or
volunteering subjects.
Studies will be designed like normal MR physics research. This includes:
1. Defining a research goal
Based on their own experiences, experiences of radiologists, clinical
researchers, or cognitive researches, a certain artifact of a current protocol
or a development request for a new MRI technique will be identified and an
approach to solve this research question will be developed.
2. Improvements in acquisition-parameters or pulse sequence
Elimination of artifacts and development of new applications in MRI can most
often be resolved by means of tuning of acquisition parameters. Based on the
hypotheses of the origin of the artifacts or the required information,
optimization of acquisition parameters is performed in vivo by systematically
changing the MR parameters involved (an MRI scanner has more than 100
parameters accessible even to a normal technician, on the next level accessible
only to MR physicists this number increases by approximately a factor of 10).
Such optimization procedures should be performed in several subjects to obtain
robust settings that are subject independent.
Whenever tuning of acquisition parameters does not yield the necessary results,
redesign of the pulse sequence should be performed. This may involve compiling
a new software version of the scanner. New pulse sequences are always first
tested in phantoms, before being tested and optimized in vivo. After each step
in the optimization process, a quality survey will be performed, for example in
collaboration with a radiologist.
3. Evaluation study
Finally, a newly developed sequence should be subject of a small pilot study
and compared to the starting sequence, to a physiological test (e.g. detection
of brain activity) or literature values. This will show whether the quality is
sufficient for clinical research and/or patient care and may form the basis for
an article in a scientific journal. Pilot studies will be limited to a maximum
of 20 subjects.

MRI is a completely safe modality. Subjects will be in the scanner for
approximately 1 hour.